The CAN bus system is used in the networking of devices for communication, for example in a vehicle, and is very well-suited for many other communication applications due to its parallel topology. In the CAN bus system, messages are transmitted using the CAN protocol, as described in the CAN specification in ISO 11898.
Recently, for this purpose in addition technologies have been proposed such as CAN-FD, with which messages can be transmitted in accordance with the specification “CAN with Flexible Data Rate, Specification Version 1.0,” (source: http://www.semiconductors.bosch.de), etc. In such technologies, the maximum possible data rate is increased beyond the value of 1 Mbit/s through the use of a higher clock rate in the region of the data fields. Due to the constantly increasing volume of data in the bus system, through the introduction of CAN-FD the migration of existing control devices and vehicle platforms to higher data rates is enabled.
In the transmission of the signals on the bus system, depending on the data to be transmitted switching takes place between a high and a low signal state, or vice versa, the high signal state also being designated the dominant state and the low signal state also being designated the recessive state. Here, a signal transmitted on the bus, the bus signal, is delayed relative to a transmit signal of a subscriber station of the bus system. In addition, at a further subscriber station of the bus system a receive signal is delayed relative to the bus signal that results due to the transmit signal.
If, for example, the transmit signal is switched from the dominant state to the recessive state, then the signal at the bus requires a delay time t11 that can also be designated t_Neg_Transmitter, in order also to switch over from the dominant state to the recessive state. Likewise, the receive signal requires, after the switching over of the signal at the bus, a time t12 that can also be designated t_Neg_Receiver, in order likewise to switch over from the dominant state to the recessive state. If the transmit signal is again switched from the recessive state to the dominant state, then the signal at the bus requires a time t13 that can also be designated t_Pos_Transmitter, in order likewise to switch over from the recessive state to dominant state. Likewise, after switching over of the bus signal the receive signal requires a time t14, which can also be designated t_Pos_Receiver, also in order to switch again from the recessive state to the dominant state.
Ideally, in the example described above t_Pos=t_Neg, such that
t_Pos=t_Pos_Transmitter+t_Pos_Receiver, and
t_Neg=t_Neg_Transmitter+t_Neg_Receiver.
However, it is problematic that as the bit rate increases, thus, for example, in the transition from CAN to CAN-FD, this ideal is increasingly departed from. A consequence of this is that the bit symmetry required for the signal is not maintained, resulting in errored transmissions in the bus system.